Morphology and properties of brain endothelial cells

Meta-analysis of the make-up and properties of in vitro models of the healthy and diseased blood-brain barrier

In vitro models of the human blood-brain barrier (BBB) are increasingly used to develop therapeutics that can cross the BBB for treating diseases of the central nervous system. Here we report a meta-analysis of the make-up and properties of transwell and microfluidic models of the healthy BBB and of BBBs in glioblastoma, Alzheimer's disease, Parkinson's disease and inflammatory diseases. We found that the type of model, the culture method (static or dynamic), the cell types and cell ratios, and the biomaterials employed as extracellular matrix are all crucial to recapitulate the low permeability and high expression of tight-junction proteins of the BBB, and to obtain high trans-endothelial electrical resistance. Specifically, for models of the healthy BBB, the inclusion of endothelial cells and pericytes as well as physiological shear stresses (~10-20 dyne cm-2) are necessary, and when astrocytes are added, astrocytes or pericytes should outnumber endothelial cells. We expect this meta-analysis to facilitate the design of increasingly physiological models of the BBB.

Evidence Implicating Blood-Brain Barrier Impairment in the Pathogenesis of Acquired Epilepsy following Acute Organophosphate Intoxication

Organophosphate (OP) poisoning can trigger cholinergic crisis, a life-threatening toxidrome that includes seizures and status epilepticus. These acute toxic responses are associated with persistent neuroinflammation and spontaneous recurrent seizures (SRS), also known as acquired epilepsy. Blood-brain barrier (BBB) impairment has recently been proposed as a pathogenic mechanism linking acute OP intoxication to chronic adverse neurologic outcomes. In this review, we briefly describe the cellular and molecular components of the BBB, review evidence of altered BBB integrity following acute OP intoxication, and discuss potential mechanisms by which acute OP intoxication may promote BBB dysfunction. We highlight the complex interplay between neuroinflammation and BBB dysfunction that suggests a positive feedforward interaction. Lastly, we examine research from diverse models and disease states that suggest mechanisms by which loss of BBB integrity may contribute to epileptogenic processes. Collectively, the literature identifies BBB impairment as a convergent mechanism of neurologic disease and justifies further mechanistic research into how acute OP intoxication causes BBB impairment and its role in the pathogenesis of SRS and potentially other long-term neurologic sequelae. Such research is critical for evaluating BBB stabilization as a neuroprotective strategy for mitigating OP-induced epilepsy and possibly seizure disorders of other etiologies. SIGNIFICANCE STATEMENT: Clinical and preclinical studies support a link between blood-brain barrier (BBB) dysfunction and epileptogenesis; however, a causal relationship has been difficult to prove. Mechanistic studies to delineate relationships between BBB dysfunction and epilepsy may provide novel insights into BBB stabilization as a neuroprotective strategy for mitigating epilepsy resulting from acute organophosphate (OP) intoxication and non-OP causes and potentially other adverse neurological conditions associated with acute OP intoxication, such as cognitive impairment.

Key brain cell interactions and contributions to the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide, with the two major hallmarks being the deposition of extracellular β-amyloid (Aβ) plaques and of intracellular neurofibrillary tangles (NFTs). Additionally, early pathological events such as cerebrovascular alterations, a compromised blood-brain barrier (BBB) integrity, neuroinflammation and synaptic dysfunction, culminate in neuron loss and cognitive deficits. AD symptoms reflect a loss of neuronal circuit integrity in the brain; however, neurons do not operate in isolation. An exclusively neurocentric approach is insufficient to understand this disease, and the contribution of other brain cells including astrocytes, microglia, and vascular cells must be integrated in the context. The delicate balance of interactions between these cells, required for healthy brain function, is disrupted during disease. To design successful therapies, it is critical to understand the complex brain cellular connections in AD and the temporal sequence of their disturbance. In this review, we discuss the interactions between different brain cells, from physiological conditions to their pathological reactions in AD, and how this basic knowledge can be crucial for developing new therapeutic strategies.

Advancements in drug delivery methods for the treatment of brain disease

The blood-brain barrier (BBB) presents a formidable obstacle to the effective delivery of systemically administered pharmacological agents to the brain, with ~5% of candidate drugs capable of effectively penetrating the BBB. A variety of biomaterials and therapeutic delivery devices have recently been developed that facilitate drug delivery to the brain. These technologies have addressed many of the limitations imposed by the BBB by: (1) designing or modifying the physiochemical properties of therapeutic compounds to allow for transport across the BBB; (2) bypassing the BBB by administration of drugs via alternative routes; and (3) transiently disrupting the BBB (BBBD) using biophysical therapies. Here we specifically review colloidal drug carrier delivery systems, intranasal, intrathecal, and direct interstitial drug delivery methods, focused ultrasound BBBD, and pulsed electrical field induced BBBD, as well as the key features of BBB structure and function that are the mechanistic targets of these approaches. Each of these drug delivery technologies are illustrated in the context of their potential clinical applications and limitations in companion animals with naturally occurring intracranial diseases.

Blood-Brain Barrier Overview: Structural and Functional Correlation

The blood-brain barrier (BBB) is a semipermeable and extremely selective system in the central nervous system of most vertebrates, that separates blood from the brain's extracellular fluid. It plays a vital role in regulating the transport of necessary materials for brain function, furthermore, protecting it from foreign substances in the blood that could damage it. In this review, we searched in Google Scholar, Pubmed, Web of Science, and Saudi Digital Library for the various cells and components that support the development and function of this barrier, as well as the different pathways to transport the various molecules between blood and the brain. We also discussed the aspects that lead to BBB dysfunction and its neuropathological consequences, with the identification of some of the most important biomarkers that might be used as a biomarker to predict the BBB disturbances. This comprehensive overview of BBB will pave the way for future studies to focus on developing more specific targeting systems in material delivery as a future approach that assists in combinatorial therapy or nanotherapy to destroy or modify this barrier in pathological conditions such as brain tumors and brain stem cell carcinomas.

The Protective Effects of AT2R Agonist, CGP42112A, Against Angiotensin II-Induced Oxidative Stress and Inflammatory Response in Astrocytes: Role of AT2R/PP2A/NFκB/ROS Signaling

Angiotensin II receptor type 2 (AT2R) agonists have been known to promote neuroprotection by limiting ischemic insult, neuronal proliferation, and differentiation. Further, AT2R agonists have also been associated with the suppression of neuroinflammation and neurodegeneration. Of note, brain astrocytes play a critical role in these neuroinflammatory and neurodegenerative processes. However, the role of AT2R in astrocytic activation remains elusive. Therefore, this study evaluated the role and molecular mechanism of AT2R agonist CGP42112A (CGP) against Angiotensin II (Ang II)-induced astrocytic activation in primary astrocytes, and in a rat model of hypertension. Here, we demonstrated that AT2R activation by CGP abrogated Ang II-induced astrocytic activation, by mitigating the ROS production, mitochondrial dysfunction, IκB-α degradation, NFκB nuclear translocation, and release of TNF-α in astrocytes. However, AT2R-mediated anti-inflammatory effects were reversed by AT2R antagonist, PD123319 (PD), in both in vitro and in vivo conditions. Mechanistically, AT2R via protein phosphatase-2A (PP2A) abrogated the Ang II-induced NFκB activation, ROS generation, and subsequent astrocytic activation. Importantly, PP2A antagonist, okadaic acid, reversed the anti-inflammatory effects of AT2R in Ang II-stimulated primary astrocytes and in the cortex of hypertensive rats. Thus, the present study suggests that AT2R by activating PP2A inhibits oxidative stress and NFκB activation, thereby preventing the astrocytic pro-inflammatory activation. Therefore, AT2R might be advantageous therapeutic target for neuroinflammatory/neurodegenerative diseases perpetuated by astrocytic activation.

Miniaturization and Automation of a Human In Vitro Blood-Brain Barrier Model for the High-Throughput Screening of Compounds in the Early Stage of Drug Discovery

Central nervous system (CNS) diseases are one of the top causes of death worldwide. As there is a difficulty of drug penetration into the brain due to the blood–brain barrier (BBB), many CNS drugs treatments fail in clinical trials. Hence, there is a need to develop effective CNS drugs following strategies for delivery to the brain by better selecting them as early as possible during the drug discovery process. The use of in vitro BBB models has proved useful to evaluate the impact of drugs/compounds toxicity, BBB permeation rates and molecular transport mechanisms within the brain cells in academic research and early-stage drug discovery. However, these studies that require biological material (animal brain or human cells) are time-consuming and involve costly amounts of materials and plastic wastes due to the format of the models. Hence, to adapt to the high yields needed in early-stage drug discoveries for compound screenings, a patented well-established human in vitro BBB model was miniaturized and automated into a 96-well format. This replicate met all the BBB model reliability criteria to get predictive results, allowing a significant reduction in biological materials, waste and a higher screening capacity for being extensively used during early-stage drug discovery studies.

Response of the cerebral vasculature to systemic carbon monoxide administration-Regional differences and sexual dimorphism

Previous studies about the modulation of the vasculature by CO were performed exclusively in male or sexually immature animals. Understanding the sex differences regarding systemic drug processing and pharmacodynamics is an important feature for safety assessment of drug dosing and efficacy. In this work, we used CORM-A1 as source of CO to examine the effects of this gasotransmitter on brain perfusion and the sex-dependent differences. Dynamic contrast-enhanced imaging (DCE)-based analysis was used to characterize the properties of CO in the modulation of cerebral vasculature in vivo, in adult C57BL/6 healthy mice. Perfusion of the temporal muscle, maxillary vein and in hippocampus, cortex and striatum was analysed for 108 min following CORM-A1 administration of 3 or 5 mg/kg. Under control conditions, brain perfusion was lower in females when compared with males. Under CO treatment, females showed a surprisingly overall reduced perfusion compared with controls (F = 3.452, p = .0004), while no major alterations (or even the expected increase) were observed in males. Cortical structures were only modulated in females. A striking female-dominated vasoconstriction effect was observed in the hippocampus and striatum following administration of CO, in this mixed-sex cohort. As these two regions are implicated in episodic and procedural memory formation, CO may have a relevant impact in learning and memory.

Microphysiological systems for recapitulating physiology and function of blood-brain barrier

Central nervous system (CNS) diseases are emerging as a major issue in an aging society. Although extensive research has focused on the development of CNS drugs, the limited transport of therapeutic agents across the blood-brain barrier (BBB) remains a major challenge. Conventional two-dimensional culture dishes do not recapitulate in vivo physiology and real-time observations of molecular transport are not possible in animal models. Recent advances in engineering techniques have enabled the generation of more physiologically relevant in vitro BBB models, and their applications have expanded from fundamental biological research to practical applications in the pharmaceutical industry. In this article, we provide an overview of recent advances in the development of in vitro BBB models, with a particular focus on the recapitulation of BBB function. The development of biomimetic BBB models is postulated to revolutionize not only fundamental biological studies but also drug screening.

The extracellular matrix of the blood-brain barrier: structural and functional roles in health, aging, and Alzheimer's disease

There is increasing interest in defining the location, content, and role of extracellular matrix (ECM) components in brain structure and function during development, aging, injury, and neurodegeneration. Studies in vivo confirm brain ECM has a dynamic composition with constitutive and induced alterations that impact subsequent cell-cell and cell-matrix interactions. Moreover, it is clear that for any given ECM component, the brain region, and cell type within that location, determines the direction, magnitude, and composition of those changes. This review will examine the ECM at the neurovascular unit (NVU) and the blood-brain barrier (BBB) within the NVU. The discussion will begin at the glycocalyx ECM on the luminal surface of the vasculature, and progress to the abluminal side with a focus on changes in basement membrane ECM during aging and neurodegeneration.

[Consideration for future in vitro BBB models - technical development to investigate the drug delivery to the CNS]

Blood vessels in the central nervous system (CNS) limit the material exchange between blood and parenchyma by blood brain barrier (BBB). At present, no appropriate in vitro BBB models are available for the investigation whether or not the candidate compounds for new drugs could be delivered to the CNS. This causes huge difficulties of the development of CNS drugs and prediction of CNS adverse effects. In this review, I first outline the structures and functions of BBB, together with the parameters used for the quantification of BBB functions. I also introduce the history of in vitro BBB models used in the drug development so far, i.e., the transition from non-cell models to the models using primary culture of rodent cells, porcine, bovine, cell lines, etc. More recently, the application of human cells differentiated from human induced pluripotent stem cells and microfluidic engineering have already started. BBB is essential for the maintenance of brain homeostasis and the mechanisms of the BBB development will be clarified by reproducing functional BBB on the dish. The new in vitro models and the data may provide accurate prediction of drug delivery to the CNS and the improvement of the evaluation system for toxicity and safety, thereby leading to successful launch of new drugs on the market.

Blood-brain barrier (BBB) and the complement landscape

The brain is an immune privileged organ, uniquely placed in the body. Two systems involved in maintaining brain homeostasis and in protecting the brain are the blood-brain barrier (BBB) and the complement system. The BBB is present in the vasculature of the brain and is the dynamic interface between brain and body that regulates what enters and leaves the brain, thereby maintaining the brain microenvironment optimal for brain function. The complement system is ubiquitous, being present systemically and in the brain, both membrane bound and in circulation. It is an important arm of the body's defense that helps maintain homeostasis by eliminating debris and damaged cells, participating in destroying pathogens, promoting inflammation and conveying 'danger signals'. Recent studies reveal that the complement system plays an important role in normal brain development. However, when the complement system is overwhelmed, complement activation could contribute to loss of BBB integrity resulting in brain pathology. Studies support an association between complement proteins and BBB dysfunction, with the mechanisms being slowly unraveled. This review will provide an overview of both these systems, how they intersect and interact with each other.

Neonatal systemic inflammation and the risk of low scores on measures of reading and mathematics achievement at age 10 years among children born extremely preterm

BACKGROUND

Difficulties with reading and math occur more commonly among children born extremely preterm than among children born at term. Reasons for this are unclear.

METHODS

We measured the concentrations of 27 inflammatory-related and neurotrophic/angiogenic proteins (angio-neurotrophic proteins) in multiple blood specimens collected a week apart during the first postnatal month from 660 children born before the 28th week of gestation who at age 10 years had an IQ ≥ 70 and a Wechsler Individual Achievement Test 3rd edition (WIAT-III) assessment. We identified four groups of children, those who had a Z-score ≤ -1 on the Word Reading assessment only, on the Numerical Operations assessment only, on both of these assessments, and on neither, which served as the referent group. We then modeled the risk of each learning limitation associated with a top quartile concentration of each protein, and with high and lower concentrations of multiple proteins.

RESULTS

The protein profile of low reading scores was confined to the third and fourth postnatal weeks when increased risks were associated with high concentrations of IL-8 and ICAM-1 in the presence of low concentrations of angio-neurotrophic proteins. The profile of low math scores was very similar, except it did not include ICAM-1. In contrast, the profile of low scores on both assessments was present in each of the first four postnatal weeks. The increased risks associated with high concentrations of TNF-α in the first two weeks and of IL-8 and ICAM-1 in the next two weeks were modulated down by high concentrations of angio-neurotrophic proteins.

CONCLUSIONS

High concentrations of angio-neurotrophic proteins appear to reduce/moderate the risk of each learning limitation associated with systemic inflammation. The three categories of limitations have protein profiles with some similarities, and yet some differences, too.

Chronic sleep restriction disrupts interendothelial junctions in the hippocampus and increases blood-brain barrier permeability

Chronic sleep loss in the rat increases blood-brain barrier permeability to Evans blue and FITC-dextrans in almost the whole brain and sleep recovery during short periods restores normal blood-brain barrier permeability. Sleep loss increases vesicle density in hippocampal endothelial cells and decreases tight junction protein expression. However, at the ultrastructural level the effect of chronic sleep loss on interendothelial junctions is unknown. In this study we characterised the ultrastructure of interendothelial junctions in the hippocampus, the expression of tight junction proteins, and quantified blood-brain barrier permeability to fluorescein-sodium after chronic sleep restriction. Male Wistar rats were sleep restricted using the modified multiple platform method during 10 days, with a daily schedule of 20-h sleep deprivation plus 4-h sleep recovery at their home-cages. At the 10th day hippocampal samples were obtained immediately at the end of the 20-h sleep deprivation period, and after 40 and 120 min of sleep recovery. Samples were processed for transmission electron microscopy and western blot. Chronic sleep restriction increased blood-brain barrier permeability to fluorescein-sodium, and decreased interendothelial junction complexity by increasing the frequency of less mature end-to-end and simply overlap junctions, even after sleep recovery, as compared to intact controls. Chronic sleep loss also induced the formation of clefts between narrow zones of adjacent endothelial cell membranes in the hippocampus. The expression of claudin-5 and actin decreased after chronic sleep loss as compared to intact animals. Therefore, it seems that chronic sleep loss disrupts interendothelial junctions that leads to blood-brain barrier hyperpermeability in the hippocampus.

Metal Nanoparticles as Targeted Carriers Circumventing the Blood-Brain Barrier

Metal nanoparticles have been proposed as a carrier and a therapeutic agent in biomedical field because of their unique physiochemical properties. Due to these physicochemical properties, they can be used in different fields of biomedicine. In relation to this, plasmonic nanoparticles can be used for detection and photothermal destruction of tumor cells or toxic protein aggregates, and magnetic iron nanoparticles can be used for imaging and for hyperthermia of tumor cells. In addition, both therapy and imaging can be combined in one nanoparticle system, in a process called theranostics. Metal nanoparticles can be synthesized to modulate their size and shape, and conjugated with different ligands, which allow their application in drug delivery, diagnostics, and treatment of central nervous system diseases. This review is focused on the potential applications of metal nanoparticles and their capability to circumvent the blood-brain barrier (BBB). Although many articles have demonstrated delivery of metal nanoparticles to the brain by crossing the BBB after systemic administration, the percentage of the injected dose that reaches this organ is low in comparison to others, especially the liver and spleen. In connection with this drawback, we elaborate the architecture of the BBB and review possible mechanisms to cross this barrier by engineered nanoparticles. The potential uses of metal nanoparticles for treatment of disorders as well as related neurotoxicological considerations are also discussed. Finally, we bring up for discussion a direct and relatively simpler solution to the problem. We discuss this in detail after having proposed the use of the intranasal administration route as a way to circumvent the BBB. This route has not been extensively studied yet for metal nanoparticles, although it could be used as a research tool for mechanistic understanding and toxicity as well as an added value for medical practice.

Tissue Non-specific Alkaline Phosphatase (TNAP) in Vessels of the Brain

The microvessels of the brain represent around 3-4 % of the brain compartment but constitute the most important length (400 miles) and surface of exchange (20 m(2)) between the blood and the parenchyma of brain. Under influence of surrounding tissues, the brain microvessel endothelium expresses a specific phenotype that regulates and restricts the entry of compounds and cells from blood to brain, and defined the so-called blood-brain barrier (BBB). Evidences that alkaline phosphatase (AP) is a characteristic feature of the BBB phenotype that allows differentiating capillary endothelial cells from brain to those of the periphery have rapidly emerge. Thenceforth, AP has been rapidly used as a biomarker of the blood-brain barrier phenotype. In fact, brain capillary endothelial cells (BCECs) express exclusively tissue non-specific alkaline phosphatase (TNAP). There are several lines of evidence in favour of an important role for TNAP in brain function. TNAP is thought to be responsible for the control of transport of some compounds across the plasma membrane of the BCECs. Here, we report that levamisole-mediated inhibition of TNAP provokes an increase of the permeability to Lucifer Yellow of the endothelial monolayer. Moreover, we illustrate the disruption of the cytoskeleton organization. Interestingly, all observed effects were reversible 24 h after levamisole removal and correlated with the return of a full activity of the TNAP. This reversible effect remains to be studied in details to evaluate the potentiality of a levamisole treatment to enhance the entry of drugs in the brain parenchyma.

Blood-brain barrier dysfunction following traumatic brain injury

Traumatic brain injury is a serious cause of morbidity and mortality worldwide. After traumatic brain injury, the blood-brain barrier, the protective barrier between the brain and the intravascular compartment, becomes dysfunctional, leading to leakage of proteins, fluid, and transmigration of immune cells. As this leakage has profound clinical implications, including edema formation, elevated intracranial pressure and decreased perfusion pressure, much interest has been paid to better understanding the mechanisms responsible for these events. Various molecular pathways and numerous mediators have been found to be involved in the intricate process of regulating blood-brain barrier permeability following traumatic brain injury. This review provides an update to the existing knowledge about the various pathophysiological pathways and advancements in the field of blood-brain barrier dysfunction and hyperpermeability following traumatic brain injury, including the role of various tight junction proteins involved in blood-brain barrier integrity and regulation. We also address pitfalls of existing systems and propose strategies to improve the various debilitating functional deficits caused by this progressive epidemic.

Peptides and proteins used to enhance gold nanoparticle delivery to the brain: preclinical approaches

An exciting and emerging field in nanomedicine involves the use of gold nanoparticles (AuNPs) in the preclinical development of new strategies for the treatment and diagnosis of brain-related diseases such as neurodegeneration and cerebral tumors. The treatment of many brain-related disorders with AuNPs, which possess useful physical properties, is limited by the blood–brain barrier (BBB). The BBB highly regulates the substances that can permeate into the brain. Peptides and proteins may represent promising tools to improve the delivery of AuNPs to the central nervous system (CNS). In this review, we summarize the potential applications of AuNPs to CNS disorders, discuss different strategies based on the use of peptides or proteins to improve the delivery of AuNPs to the brain, and examine the intranasal administration route, which bypasses the BBB. We also analyze the potential neurotoxicity of AuNPs and the perspectives and new challenges concerning the use of peptides and proteins to enhance the delivery of AuNPs to the brain. The majority of the work described in this review is in a preclinical stage of experimentation, or in select cases, in clinical trials in humans. We note that the use of AuNPs still requires substantial study before being translated into human applications. However, for further clinical research, the issues related to the potential use of AuNPs must be analyzed.

Astrocyte morphology, heterogeneity, and density in the developing African giant rat (Cricetomys gambianus)

Astrocyte morphologies and heterogeneity were described in male African giant rats (AGR; Cricetomys gambianus, Waterhouse) across three age groups (five neonates, five juveniles, and five adults) using Silver impregnation method and immunohistochemistry against glial fibrillary acidic protein. Immunopositive cell signaling, cell size and population were least in neonates, followed by adults and juveniles, respectively. In neonates, astrocyte processes were mostly detected within the glia limitans of the mid and hind brain; their cell bodies measuring 32 ± 4.8 μm in diameter against 91 ± 5.4 μm and 75 ± 1.9 μm in juveniles and adults, respectively. Astrocyte heterogeneity in juvenile and adult groups revealed eight subtypes to include fibrous astrocytes chiefly in the corpus callosum and brain stem, protoplasmic astrocytes in the cortex and dentate gyrus (DG); radial glia were found along the olfactory bulb (OB) and subventricular zone (SVZ); velate astrocytes were mainly found in the cerebellum and hippocampus; marginal astrocytes close to the pia mater; Bergmann glia in the molecular layer of the cerebellum; perivascular and periventricular astrocytes in the cortex and third ventricle, respectively. Cell counts from twelve anatomical regions of the brain were significantly higher in juveniles than in adults (p ≤ 0.01) using unpaired student t-test in the cerebral cortex, pia, corpus callosum, rostral migratory stream, DG, and cerebellum. Highest astrocyte count was found in the DG, while the least count was in the brain stem and sub cortex. Astrocytes along the periventricular layer of the OB are believed to be part of the radial glia system that transport newly formed cells towards the hippocampus and play roles in neurogenesis migration and homeostasis in the AGR. Therefore, astrocyte heterogeneity was examined across age groups in the AGR to determine whether age influences astrocytes population in different regions of the AGR brain and discuss possible functional roles.

The rights and wrongs of blood-brain barrier permeability studies: a walk through 100 years of history

Careful examination of relevant literature shows that many of the most cherished concepts of the blood-brain barrier are incorrect. These include an almost mythological belief in its immaturity that is unfortunately often equated with absence or at least leakiness in the embryo and fetus. The original concept of a blood-brain barrier is often attributed to Ehrlich; however, he did not accept that permeability of cerebral vessels was different from other organs. Goldmann is often credited with the first experiments showing dye (trypan blue) exclusion from the brain when injected systemically, but not when injected directly into it. Rarely cited are earlier experiments of Bouffard and of Franke who showed methylene blue and trypan red stained all tissues except the brain. The term “blood-brain barrier” “Blut-Hirnschranke” is often attributed to Lewandowsky, but it does not appear in his papers. The first person to use this term seems to be Stern in the early 1920s. Studies in embryos by Stern and colleagues, Weed and Wislocki showed results similar to those in adult animals. These were well-conducted experiments made a century ago, thus the persistence of a belief in barrier immaturity is puzzling. As discussed in this review, evidence for this belief, is of poor experimental quality, often misinterpreted and often not properly cited. The functional state of blood-brain barrier mechanisms in the fetus is an important biological phenomenon with implications for normal brain development. It is also important for clinicians to have proper evidence on which to advise pregnant women who may need to take medications for serious medical conditions. Beliefs in immaturity of the blood-brain barrier have held the field back for decades. Their history illustrates the importance of taking account of all the evidence and assessing its quality, rather than selecting papers that supports a preconceived notion or intuitive belief. This review attempts to right the wrongs. Based on careful translation of original papers, some published a century ago, as well as providing discussion of studies claiming to show barrier immaturity, we hope that readers will have evidence on which to base their own conclusions.

Astrocytic modulation of blood brain barrier: perspectives on Parkinson's disease

The blood–brain barrier (BBB) is a tightly regulated interface in the Central Nervous System (CNS) that regulates the exchange of molecules in and out from the brain thus maintaining the CNS homeostasis. It is mainly composed of endothelial cells (ECs), pericytes and astrocytes that create a neurovascular unit (NVU) with the adjacent neurons. Astrocytes are essential for the formation and maintenance of the BBB by providing secreted factors that lead to the adequate association between the cells of the BBB and the formation of strong tight junctions. Under neurological disorders, such as chronic cerebral ischemia, brain trauma, Epilepsy, Alzheimer and Parkinson’s Diseases, a disruption of the BBB takes place, involving a lost in the permeability of the barrier and phenotypical changes in both the ECs and astrocytes. In this aspect, it has been established that the process of reactive gliosis is a common feature of astrocytes during BBB disruption, which has a detrimental effect on the barrier function and a subsequent damage in neuronal survival. In this review we discuss the implications of astrocyte functions in the protection of the BBB, and in the development of Parkinson’s disease (PD) and related disorders. Additionally, we highlight the current and future strategies in astrocyte protection aimed at the development of restorative therapies for the BBB in pathological conditions.

Neuropsychiatric Lupus, the Blood Brain Barrier, and the TWEAK/Fn14 Pathway

Patients with systemic lupus erythematosus (SLE) can experience acute neurological events such as seizures, cerebrovascular accidents, and delirium, psychiatric conditions including depression, anxiety, and psychosis, as well as memory loss and general cognitive decline. Neuropsychiatric SLE (NPSLE) occurs in between 30 and 40% of SLE patients, can constitute the initial patient presentation, and may occur outside the greater context of an SLE flare. Current efforts to elucidate the mechanistic underpinnings of NPSLE are focused on several different and potentially complementary pathways, including thrombosis, brain autoreactive antibodies, and complement deposition. Furthermore, significant effort is dedicated to understanding the contribution of neuroinflammation induced by TNF, IL-1, IL-6, and IFN-γ. More recent studies have pointed to a possible role for the TNF family ligand TWEAK in the pathogenesis of neuropsychiatric disease in human lupus patients, and in a murine model of this disease. The blood brain barrier (BBB) consists of tight junctions between endothelial cells (ECs) and astrocytic projections which regulate paracellular and transcellular flow into the central nervous system (CNS), respectively. Given the privileged environment of the CNS, an important question is whether and how the integrity of the BBB is compromised in NPSLE, and its potential pathogenic role. Evidence of BBB violation in NPSLE includes changes in the albumin quotient (Q_alb) between plasma and cerebrospinal fluid, activation of brain ECs, and magnetic resonance imaging. This review summarizes the evidence implicating BBB damage as an important component in NPSLE development, occurring via damage to barrier integrity by environmental triggers such as infection and stress; cerebrovascular ischemia as result of a generally prothrombotic state; and immune mediated EC activation, mediated by antibodies and/or inflammatory cytokines. Additionally, new evidence supporting the role of TWEAK/Fn14 signaling in compromising the integrity of the BBB in lupus will be presented.

Shuttle-mediated nanoparticle delivery to the blood-brain barrier

Many therapeutic drugs are excluded from entering the brain due to their lack of transport through the blood-brain barrier (BBB). The development of new strategies for enhancing drug delivery to the brain is of great importance in diagnostics and therapeutics of central nervous diseases. To overcome this problem, a viral fusion peptide (gH625) derived from the glycoprotein gH of Herpes simplex virus type 1 is developed, which possesses several advantages including high cell translocation potency, absence of toxicity of the peptide itself, and the feasibility as an efficient carrier for delivering therapeutics. Therefore, it is hypothesized that brain delivery of nanoparticles conjugated with gH625 should be efficiently enhanced. The surface of fluorescent aminated polystyrene nanoparticles (NPs) is functionalized with gH625 via a covalent binding procedure, and the NP uptake mechanism and permeation across in vitro BBB models are studied. At early incubation times, the uptake of NPs with gH625 by brain endothelial cells is greater than that of the NPs without the peptide, and their intracellular motion is mainly characterized by a random walk behavior. Most importantly, gH625 peptide decreases NP intracellular accumulation as large aggregates and enhances the NP BBB crossing. In summary, these results establish that surface functionalization with gH625 may change NP fate by providing a good strategy for the design of promising carriers to deliver drugs across the BBB for the treatment of brain diseases.

TNAP and EHD1 are over-expressed in bovine brain capillary endothelial cells after the re-induction of blood-brain barrier properties

Although the physiological properties of the blood-brain barrier (BBB) are relatively well known, the phenotype of the component brain capillary endothelial cells (BCECs) has yet to be described in detail. Likewise, the molecular mechanisms that govern the establishment and maintenance of the BBB are largely unknown. Proteomics can be used to assess quantitative changes in protein levels and identify proteins involved in the molecular pathways responsible for cellular differentiation. Using the well-established in vitro BBB model developed in our laboratory, we performed a differential nano-LC MALDI-TOF/TOF-MS study of Triton X-100-soluble protein species from bovine BCECs displaying either limited BBB functions or BBB functions re-induced by glial cells. Due to the heterogeneity of the crude extract, we increased identification yields by applying a repeatable, reproducible fractionation process based on the proteins' relative hydrophobicity. We present proteomic and biochemical evidence to show that tissue non-specific alkaline phosphatase (TNAP) and Eps15 homology domain-containing protein 1(EDH1) are over-expressed by bovine BCECs after the re-induction of BBB properties. We discuss the impact of these findings on current knowledge of endothelial and BBB permeability.

Nanoparticles and spermatogenesis: how do nanoparticles affect spermatogenesis and penetrate the blood-testis barrier

Due to the widespread use of nanomaterials in medical, industrial and military applications, the question as to whether nanoparticles (NPs) cause harmful disturbances in human health, especially on the reproductive system, remains a matter of concern. In this review, we focus mainly on the in vivo and in vitro effects of NPs on spermatogenesis at the clinical, cellular and molecular levels. In general, most NPs display adverse effects on spermatogenesis at these various levels; but, some NPs show no adverse effects. However, the mechanism underlying NP disruption of spermatogenesis and penetration of the blood-testis barrier remains unclear. In this review, we raise many hypotheses for experimental testing in order to elucidate the mechanism.